IO: Fix socket priority

On Linux, setting the ToS will also set the priority and the range of
accepted values is quite limited (masked by 0x1e). Therefore, 0xc0 is
translated to a priority of 0, not something we want, overriding the
"7" priority which was set previously explicitely. To avoid that, just
move setting priority later in the code.

Thanks to Vincent Bernat for the patch.
49 jobs from master in 9 minutes and 10 seconds (queued for 13 seconds)
Status Job ID Name Coverage
  Image
passed #101670
dind allowed to fail
docker_centos-6-amd64

00:00:32

passed #101671
dind allowed to fail
docker_centos-7-amd64

00:00:30

passed #101660
dind allowed to fail
docker_debian-7-amd64

00:01:19

passed #101664
dind allowed to fail
docker_debian-7-i386

00:01:04

passed #101661
dind allowed to fail
docker_debian-8-amd64

00:01:11

passed #101665
dind allowed to fail
docker_debian-8-i386

00:01:04

passed #101662
dind allowed to fail
docker_debian-9-amd64

00:01:10

passed #101666
dind allowed to fail
docker_debian-9-i386

00:01:04

passed #101663
dind allowed to fail
docker_debian-testing-amd64

00:01:09

passed #101667
dind allowed to fail
docker_debian-testing-i386

00:00:57

passed #101668
dind allowed to fail
docker_fedora-25-amd64

00:00:28

passed #101669
dind allowed to fail
docker_fedora-26-amd64

00:00:33

passed #101672
dind allowed to fail
docker_opensuse-42_3-amd64

00:00:26

passed #101673
dind allowed to fail
docker_ubuntu-14_04-amd64

00:00:32

passed #101674
dind allowed to fail
docker_ubuntu-16_04-amd64

00:00:32

 
  Build
passed #101687
docker linux amd64
build-centos-6-amd64

00:00:34

passed #101688
docker linux amd64
build-centos-6-amd64-v6

00:00:38

passed #101689
docker linux amd64
build-centos-7-amd64

00:00:37

passed #101690
docker linux amd64
build-centos-7-amd64-v6

00:00:40

passed #101675
docker linux amd64
build-debian-7-amd64

00:02:33

passed #101679
docker linux amd64
build-debian-7-amd64-v6

00:02:37

passed #101697
docker linux amd64
build-debian-7-i386

00:00:40

passed #101698
docker linux amd64
build-debian-7-i386-v6

00:00:42

passed #101676
docker linux amd64
build-debian-8-amd64

00:02:49

passed #101680
docker linux amd64
build-debian-8-amd64-v6

00:02:53

passed #101699
docker linux amd64
build-debian-8-i386

00:00:41

passed #101700
docker linux amd64
build-debian-8-i386-v6

00:00:44

passed #101677
docker linux amd64
build-debian-9-amd64

00:02:41

passed #101681
docker linux amd64
build-debian-9-amd64-v6

00:02:39

passed #101701
docker linux amd64
build-debian-9-i386

00:00:43

passed #101702
docker linux amd64
build-debian-9-i386-v6

00:00:46

passed #101678
docker linux amd64
build-debian-testing-amd64

00:02:39

passed #101682
docker linux amd64
build-debian-testing-amd64-v6

00:02:35

passed #101703
docker linux amd64
build-debian-testing-i386

00:00:43

passed #101704
docker linux amd64
build-debian-testing-i386-v6

00:00:35

passed #101683
docker linux amd64
build-fedora-25-amd64

00:02:33

passed #101684
docker linux amd64
build-fedora-25-amd64-v6

00:00:33

passed #101685
docker linux amd64
build-fedora-26-amd64

00:00:40

passed #101686
docker linux amd64
build-fedora-26-amd64-v6

00:00:42

passed #101705
freebsd amd64
build-freebsd-11-amd64

00:05:22

passed #101706
freebsd amd64
build-freebsd-11-amd64-v6

00:05:24

passed #101707
freebsd i386
build-freebsd-11-i386

00:05:29

passed #101708
freebsd i386
build-freebsd-i386-v6

00:05:20

passed #101691
docker linux amd64
build-opensuse-42_3-amd64

00:00:37

passed #101692
docker linux amd64
build-opensuse-42_3-amd64-v6

00:00:39

passed #101693
docker linux amd64
build-ubuntu-14_04-amd64

00:00:38

passed #101694
docker linux amd64
build-ubuntu-14_04-amd64-v6

00:00:31

passed #101695
docker linux amd64
build-ubuntu-16_04-amd64

00:00:31

passed #101696
docker linux amd64
build-ubuntu-16_04-amd64-v6

00:00:41